Hearing protectors comprise two ear cups and a device for fastening the hearing protector to the head of a wearer, such that the ear cups are positioned over the wearer's ears. Ear cups used in existing hearing protectors may function as active elements, which means that they have a passive, sound-reducing function which is combined with the function of actively reproducing sound inside the ear cup to allow the user to hear this reproduced sound.
To this end, the ear cup may be provided with an electronic unit having a speaker. The electronic unit may incorporate different functions. One type of electronic unit may, for instance, contain a radio receiver and the electronic circuitry required to reproduce the sound received by the radio receiver through the speaker. Another type of electronic unit may be designed such that it is capable of reproducing ambient sound from the vicinity of the hearing protector. In this case, the hearing protector may be provided with a microphone that is connected to the electronic unit. The electronic unit thus has a function that allows it to receive the sound from the microphone and convert it in such a manner that it is emitted by the speaker in the ear cup at a level that is suitable for the wearer. The electronic circuitry of the electronic unit may comprise, for example, circuits that dampen frequencies that are particularly disturbing to the human ear for the benefit of the frequency range within which ordinary speech is situated. In this way, the user of an active hearing protector of this kind is able to talk to another person in a noisy environment without having to remove the hearing protector and without risking any hearing damage. The electronic unit may also be designed to have both of the functions described above.
Different types of ear cups may be designed with different degrees of attenuation depending on the levels of noise in the environments in which they are to be used. If a hearing protector is intended for use in environments where noise levels are high, for example in the vicinity of aircraft taking off, the ear cup must have a much higher degree of noise attenuation than if the hearing protector is to be used in less noisy environments, for example in a catering kitchen. For this reason, hearing protectors are designed to have different noise-attenuating ability, i.e. to have noise-reducing spaces of different size. In general, the larger the cup the better the attenuating ability.
It is important that speakers arranged in hearing protectors do not emit sound that is too loud, so that it becomes harmful to the ear of the user. For this reason, there is an upper limit for the sound volume that can be emitted by the electronic unit through the speaker in the ear cup. This sound reproduction level limit is described, for instance, in the European standard EN352. To avoid that the sound level emitted by the speaker adjacent the ear of a user exceeds this limit, and to make sure that the user has the same type of sound experience with all ear cups, it is desirable for active ear cups to emit the same sound level adjacent the ear at a certain sound volume setting, independently of the type of ear cup. To achieve this in cups with different degrees of attenuation, i.e. with noise-reducing spaces of different size, different electronic circuitry must be employed today to provide the same sound-reproducing function(s) depending on the degree of attenuation of the ear cup. When manufacturing, for example, ear cups with two different degrees of attenuation, two versions of the circuitry required to provide the sound-reproducing function must be developed, one for the ear cup with a higher degree of attenuation and another for the ear cup with a lower degree of attenuation. This means higher costs for each ear cup in the form of assembly, development, adaptation of the circuitry, storage etc. than would be the case if the same circuitry could be used regardless of the degree of attenuation of the ear cup.